GB/T 20975.11-2018Methods for chemical analysis of aluminium and aluminium alloys—Part 11: Determination of lead content (English PDF)

2.1 Method principle

The test portion is dissolved with hydrochloric acid-nitric acid mixed acid. At a wavelength of 217.0 nm or 283.3 nm of an atomic absorption spectrometer, the absorbance of lead is measured with an air-acetylene lean-burn flame, and the mass fraction of lead is calculated.

2.2 Reagents and materials

Unless otherwise stated, in the analysis, only identified analytically pure reagents and Grade 3 water are used.

2.2.1 Aluminium [w(Al)>=99.99%, free of lead].

2.2.2 Nitric acid (rho=1.42 g/mL).

2.5.4.2

- When the mass fraction of lead is >0.10%~1.50%, TRANSFER the test solution (2.5.4.1) or the combined test solution after the treatment of insoluble substance into a 500 mL volumetric flask; ADD 25 mL of nitric acid (2.2.2); USE water to dilute to volume, and MIX well. The dilution factor R of the solution is 5;

- When the mass fraction of lead is >1.50%~12.0%, TRANSFER the test solution (2.5.4.1) or the combined test solution after the treatment of insoluble substance into a 500 mL volumetric flask; ADD 25 mL of nitric acid (2.2.2); USE water to dilute to volume, and MIX well. PIPETTE 10.00 mL of test solution into a 100 mL volumetric flask; ADD 5 mL of nitric acid (2.2.2); USE water to dilute to volume, and MIX well. The dilution factor R of the solution is 50.

Note: If there is insoluble substance, FILTER and WASH. The residue and the filter paper are placed in a platinum crucible, ashed (Do not burn the filter paper), fired at about 550 °C, and cooled. ADD 5 mL of hydrofluoric acid (2.2.4); and ADD nitric acid (2.2.2) dropwise until the solution is clear; HEAT to evaporate to dryness; BURN at 700 °C for several minutes, and COOL. DISSOLVE the residue with as little nitric acid (2.2.2) as possible (FILTER if necessary). This solution is combined in the previous filtrate.

2.5.4.3

The blank test solution (2.5.3) and the test solution (2.5.4.2) are, at a wavelength of 217.0 nm or 283.3 nm of the atomic absorption spectrometer, using an air-acetylene lean-burn flame, zero-setting with water, measured for the absorbance of lead. The corresponding lead content is found from the working curve.

2.5.5 Drawing of working curve

2.5.5.1 Preparation of a series of standard solutions

The preparation of this series of standard solutions, according to the mass fraction of lead, is divided into three sections.

- When the mass fraction of lead is >0.005%~0.10%. PIPETTE 0 mL, 1.00 mL, 3.00 mL, 5.00 mL, 7.00 mL, 10.00 mL of lead standard solution (2.2.8); and PLACE them in a set of 100 mL volumetric flasks. ADD 50.00 mL of aluminium solution (2.2.6) and 5 mL of nitric acid (2.2.2) respectively; USE water to dilute to volume, and MIX well;

- When the mass fraction of lead is >0.10%~1.50%. PIPETTE 0 mL, 2.00 mL, 6.00 mL, 10.00 mL of lead standard solution (2.2.8) and 1.50 mL, 2.00 mL, 2.50 mL, 3.00 mL of standard stock solution of lead (2.2.7); PLACE in a set of 100 mL volumetric flasks. ADD 10.00 mL of aluminium solution (2.2.6) and 5 mL of nitric acid (2.2.2) respectively; USE water to dilute to volume, and MIX well; […]

3.2 Reagents and materials

Unless otherwise stated, in the analysis, only identified guaranteed reagents and Grade 1 water are used.

3.2.1 Hydrochloric acid (rho=1.19 g/mL).

3.2.2 Nitric acid (rho=1.42 g/mL).

3.2.3 Hydrochloric acid (1+1).

3.2.4 Nitric acid (1+1).

3.2.6 Hydrochloric acid (2+98).

3.2.5 Mixed acid

Hydrochloric acid (3.2.3) and nitric acid (3.2.4) are mixed in a volume ratio of (3+1).

3.2.7 Potassium borohydride solution (10 g/L)

WEIGH 2.0 g of potassium borohydride and 2.2 g of potassium ferricyanide in a beaker; USE sodium hydroxide solution (12 g/L) to dilute to 200 mL, and MIX well. Prepared when used.

3.2.8 Standard stock solution of lead (1.0 mg/mL)

WEIGH 1.0000 g of lead [w(Pb)>=99.99%]; PLACE in a 250 mL beaker; ADD 10 mL of nitric acid (2.2.2); COVER the watch glass; slowly HEAT until complete dissolution; BOIL for a few minutes and COOL. TRANSFER the solution to a 1000 mL volumetric flask; USE water to dilute to volume, and MIX well. 1 mL of this solution contains 1.0 mg of lead.

3.2.9 Lead standard solution A (10 µg/mL)

PIPETTE 1.00 mL of standard stock solution of lead (3.2.8) in a 100 mL volumetric flask; USE hydrochloric acid (3.2.6) to dilute to volume, and MIX well. 1 mL of this solution contains 10 µg of lead. Prepared when used.

3.2.10 Lead standard solution B (0.1 µg/mL)

PIPETTE 1.00 mL of lead standard solution A (3.2.9) in a 100 mL volumetric flask; USE hydrochloric acid (3.2.6) to dilute to volume, and MIX well. 1 mL of this solution contains 0.1 µg of lead. Prepared when used.

3.3 Instrument

Atomic fluorescence spectrometer, with lead hollow cathode lamp.

3.4 Sample

The sample is processed into chips having a thickness of no more than 1 mm. […]